Epidemiology of cervical human papillomavirus infection

The epithelial lining of the anogenital tract is the target for infection by a group of mucosotropic viruses, the human papillomaviruses (HPV). There are more than 70 HPV types, of which nearly 30 infect the anogenital tract. Sexual behaviour and age are the most important determinants of cervical HPV infection and seem to be the most consistent findings in cross-sectional studies. A role for other variables, such as smoking, use of oral contraceptives and reproductive factors has emerged in some studies but less consistently. Recent evidence suggests that the sexual transmissibility of cervical HPV infection may vary by type. Infection with HPV types of high oncogenicity is strongly associated with sexual activity whereas low-oncogenic-risk types exhibit a weaker association with the same indicators of sexual behaviour. The age-dependence of HPV prevalence seems also to vary on the basis of oncogenicity of viral types. The negative correlation with age seems to be more pronounced for infection with low-oncogenic-risk types. Over 15% of asymptomatic women who are sexually active can have HPV detected in their cervix using amplified DNA hybridization methods. Most of these infections are transient and are probably of little significance. The concern resides, however, in the small proportion of women who harbour persistent HPV infections. Recent evidence suggests that these women stand a much greater risk of subsequent cervical neoplasia, indicating that persistent, not transient, HPV infections are the actual biological precursor in cervical carcinogenesis. Research on the epidemiology of viral persistence will help in the formation of algorithms and policies for inclusion of some form of HPV testing in cervical cancer prevention.